Monster of the Day: Afanc

Source:  Welsh Mythology and "The Scar" by China Mieville
Location:  A lake in Wales or in a transdimensional sea between all seas
Threat Assessment:  8.  In the myths the Afanc is a watery beavery crocodiley beastie that threatens everyone.  In one myth it is tempted out of his lair by a beautiful lady and is chained.  In another myth the waves for enraged afanc flooded all of Britain leaving only two people to repopulate the Island.  In the Scar it is a bigger than big beastie that a floating city yokes to provide locomotion.
Limitations:  It can be caught.  The trouble is as always when you ride a tiger (or afanc) how do you get off?